W245 CYPRESS [Cypress Semiconductor], W245 Datasheet - Page 5

• Manufacturer Part Number: W245
• Description: Frequency Multiplying, Peak Reducing EMI Solution
• Manufacturer: CYPRESS [Cypress Semiconductor]

Spread Spectrum Frequency Timing Generator
The device generates a clock that is frequency modulated in
order to increase the bandwidth that it occupies. By increasing
the bandwidth of the fundamental and its harmonics, the am-
plitudes of the radiated electromagnetic emissions are re-
duced. This effect is depicted in Figure 2.
As shown in Figure 2, a harmonic of a modulated clock has a
much lower amplitude than that of an unmodulated signal. The
reduction in amplitude is dependent on the harmonic number
and the frequency deviation or spread. The equation for the
reduction is
Document #: 38-07229 Rev. *B
dB = 6.5 + 9*log
MAX.
MIN.
Figure 2. Clock Harmonic with and without SSCG Modulation Frequency Domain Representation
10
(P) + 9*log
10
(F)
Figure 3. Typical Modulation Profile
Where P is the percentage of deviation and F is the frequency
in MHz where the reduction is measured.
The output clock is modulated with a waveform depicted in
Figure 3. This waveform, as discussed in “Spread Spectrum
Clock Generation for the Reduction of Radiated Emissions” by
Bush, Fessler, and Hardin produces the maximum reduction
in the amplitude of radiated electromagnetic emissions. The
deviation selected for this chip is as described in Table 2.
Figure 3 details the Cypress spreading pattern. Cypress does
offer options with more spread and greater EMI reduction.
Contact your local Sales representative for details on these
devices.
Spectrum
Enabled
Spread
EMI Reduction
Frequency Span (MHz)
Down Spread
W245-30
Spread
Spectrum
Non-
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